Answer:
The answer is "subtracting the average return on the U.S. Treasury bill from".
Explanation:
By subtracting the average annual return on the US Treasury bill form of the investment's average return, that excess return is calculated, when the risk premium is another term for excess return. After subtracting the risk-free return from its investment's annualized value, the risk premium is calculated its avg treasury bond investment is a risk-free portfolio.